Two genes involved in hereditary breast and ovary cancer cases

Date:

February 18, 2011

Source:

Elhuyar Fundazioa

Summary:

Between 5 and 10 percent of breast cancer cases are hereditary, arising because the patient inherits from the father or mother a mutation in a gene that is susceptible to causing the illness. BRCA1 and BRCA2 have already been identified as two of the genes to be monitored. It is estimated that 30 percent of hereditary breast cancer cases are due to mutations in one of these two genes (which suggests, at the same time, that there are other genes involved, but exactly how is still unknown). In any case, few of the mutations found in BRCA1 and BRCA2 could be clearly identified as pathological. The fact is that the mutations found were numerous; their variation even depending on the population.

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FULL STORY

Between 5 and 10 percent of breast cancer cases are hereditary, arising because the patient inherits from the father or mother a mutation in a gene that is susceptible to causing the illness. BRCA1 and BRCA2 have already been identified as two of the genes to be monitored. It is estimated that 30 percent of hereditary breast cancer cases are due to mutations in one of these two genes (which suggests, at the same time, that there are other genes involved, but exactly how is still unknown). In any case, few of the mutations found in BRCA1 and BRCA2 could be clearly identified as pathological. The fact is that the mutations found were numerous; their variation even depending on the population.

Biologist Elena Beristain has been investigating the CAPV-EAE population. Concretely, for her study she took 521 patients mainly from the Txagorritxu hospital in the Basque capital city of Vitoria-Gasteiz, and the Cruces hospital in Barakaldo, near Bilbao: 274 patients with breast or ovarian cancer (given that the latter is also associated with mutations in the BRCA1 and BRCA2 genes), 115 family relations of these, and another 132 women who acted as a control population. Ms Beristain molecularly characterised the BCRA1 y BCRA2 genes of these individuals; apart from the exon 10 of the CHEK2 gene, also associated with the illness. Her thesis was defended at the University of the Basque Country (UPV/EHU) and it is entitled, Genetic study amongst women resident in the CAPV-EAE with hereditary breast/ovary cancer.

Could rise to 12 percent

According to the results shown, different types of variations in the genes under study have been found, including pathological ones, neutral ones and those of uncertain significance. As regards the clearly pathological mutations, the frequency is 10 percent. Nevertheless, Ms Beristain stressed that, amongst those sporadic cases of under-40s, that is a especially rare condition: only in one case was a pathological mutation found. This is why she suggested discarding under-35s in this type of research, and in which case the result arrived at in her study rises from 10 percent to 12 percent. In any case, the percentages of pathological mutations found in this genetic study of the CAPV-EAE population turned out to be less than amongst other European populations.

The study has thrown up more data regarding age. For example, the percentages show that, for family-member carriers of mutation in the main genes under study, the accumulated risk of suffering breast cancer at 70 is 69 percent for the BRCA1 and 67 percent for the BRCA2. This means that penetration is not complete and there exists the possibility that this gene does not, in the end, express itself. As regards the data on gender, it is significant that masculine breast cancer is mainly associated with mutations in the BRCA2 gene.

Different mutations in the Autonomous Community of the Basque Country

The variability from population to population in mutations in general is also clear from the results of this thesis. Ms Beristain explained that a great number of alterations, hitherto unrecorded, have been found, and from this she concludes that many of the mutations found in the CAPV-EAE are different from those described for other populations. However, she explains, amongst these, no founder effect mutation was found, i.e. there has been no case of some, many or all Basque patients coming from a small population of individuals having transmitted this common genetic characteristic to all their descendents. However it may be, the new types of mutations found represent a contribution to the already existing variability.

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